Retractable safety syringe with non-loaded seal

ABSTRACT

A retractable safety syringe may have a needle, needle holder, syringe body, a shaft seal, and a plunger assembly. A proximal portion of the body and a piston of the plunger may define a vacuum chamber. The plunger assembly may comprise a shaft coupled to a piston. The shaft may have at least one non-engaging portion and at least one engaging portion. The plunger assembly is movable between a storage position and working positions. In the storage position, little or no force is exerted on the shaft seal by the non-engaging portion. In the working positions, the engaging portion is in sealing engagement with the shaft seal to seal the vacuum chamber. Stopper movement of the retractable safety syringe may be reduced or eliminated if the retractable safety syringe is prefilled.

BACKGROUND

In recent years, the public (e.g., medical personnel and healthcareproviders, drug addicts, drug users, and the like) has becomeincreasingly aware of the health hazards associated with needle reuseand accidental needle prickings. For example, at least twentyblood-borne pathogens may be transmitted by the reuse of needles oraccidental needle prickings. For example, these blood borne pathogensmay include and are not limited to Human Immunodeficiency Virus (HIV),Acquired Immunodeficiency Syndrome (AIDS), Hepatitis B, Hepatitis C,syphilis, malaria, tuberculosis, and herpes. Despite the awareness ofthe risk of needle reuse and accidental needle prickings, at least 36percent of HIV/AIDS cases and more than 50 percent of Hepatitis B andHepatitis C cases in the United States may be linked to the sharing ofneedles among drug addicts. Accordingly, there is a need to curb thepractice of sharing needles among drug addicts.

The problem of needle sharing or needle reuses is further amplified whenviewed in relation to the world population. For example, approximately30 percent of reported HIV/AIDS cases in Brazil, Chile, Uruguay,Paraguay and Argentina are directly related to the sharing ofcontaminated needles among drug addicts. Approximately 70 percent of theHIV cases reported in China are directly linked to the sharing ofcontaminated needles. In eastern European countries, 80 percent ofinjection drug addicts admit to sharing contaminated needles.Approximately 43 percent of HIV/AIDS cases reported in Poland andYugoslavia are linked to the sharing of contaminated needles among drugaddicts.

Accidental needle prickings also pose a threat to healthcare workers. Inparticular, approximately one million accidental needle prickings arereported by healthcare workers in the United States annually. However,it is believed that at least three million accidental needle prickingsoccur each year, of which about two million are unreported. Variousstudies estimate that out of all the accidental needle pricking injuriesthat occur to nurses, approximately 40 percent to 53 percent gounreported. Various studies also estimate that out of all the needlepricking injuries that occur to laboratory technicians, approximately 92percent go unreported. Various studies further estimate that out of allthe needle pricking injuries that occur to physicians, approximately 70percent to 95 percent go unreported.

In 1997, the Center for Disease Control and Prevention (CDC) sponsored astudy that found that approximately 76 percent of needle prickinginjuries could be avoided by using safety needles. Presently, there areat least 250 types of safety syringes. Unfortunately, the retractablesafety syringes that currently exist have been criticized for variousproblems associated in operating the retractable safety syringe and itsineffectiveness.

One type of safety syringe is a vacuum assisted safety syringe whereinthe needle of the syringe is retracted into a syringe body after apiston engages a needle holder due to a retraction force of a variablevacuum compartment. The refraction force of the variable vacuumcompartment is a function of the surface area of the piston as it istraversed from a retracted position to an engaged position. Varioustypes of seals may be used to create an airtight barrier around theplunger shaft. The seal or seals used to produce the variable vacuumcompartment may begin to break down, become less resilient, or otherwisefail over time or due to various environmental conditions. For example,when various components of a syringe, such as the seal, are exposed to aprolonged force, the components may conform to an undesirable shapethereby reducing the effectiveness of the component and hamper theoverall operation and function of the syringe. Additionally, the seals,or other components, of some safety syringes are prone to reactnegatively to hot climates. The exposure of these syringes to hottemperatures, cold temperatures, or temperature cycling during storageor shipment can lead to an operational failure of the syringe.

Furthermore, it is often desirable to prefill a safety syringes duringan automated process prior to shipment. The process of manufacturingprefilled syringes typically includes sterilizing the syringe. Theprefilled and sterilized syringe may then be shipped via at least oneair shipment. If the shipment of prefilled syringes is shipped a longdistance, such as to a developing country, the shipment of prefilledsyringes may be carried via numerous air shipments. During the airshipment of the prefilled syringe the prefilled syringe may be exposedto numerous changes in atmospheric pressures. In some cases, shipping aprefilled syringe via air may exposed the syringe to a reduced pressureequivalent to an elevation of approximately 8,000 feet. If a gas bubbleis present in the fluid chamber of the syringe, the gas bubble mayincrease in volume due to the decreased atmospheric pressure. As the gasbubble increases in volume, the stopper of the syringe may be proximallydisplaced, which may ultimately cause a sterility failure in thesyringe. When the syringe returns to normal atmospheric conditions, thegas bubble returns to its starting volume and the stopper will return toits original location. Thus, a visual inspection of the stopper may notindicate stopper movement has occurred and a sterility failure may havetranspired during shipment.

Accordingly, there is a need in the art for an improved safety syringe.

SUMMARY

In accordance with various embodiments <Complete upon finalization ofclaims>

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood from a detaileddescription of example embodiments taken in conjunction with thefollowing figures:

FIG. 1 is a side view of a retractable safety syringe in accordance withone non-limiting embodiment.

FIG. 2 is a cross-sectional view of the retractable safety syringe ofFIG. 1.

FIG. 3 is a cross sectional perspective view of the distal end of theretractable safety syringe with an exploded view of a braking mechanismin accordance with one non-limiting embodiment.

FIG. 4 is a perspective view of a piston of a retractable safety syringein accordance with on non-limiting embodiment.

FIG. 5 is a cross-sectional view of the piston of FIG. 4

FIG. 6 illustrates a retractable safety syringe at the conclusion of theoperational stroke.

FIGS. 7-8 illustrate shafts of a retractable safety syringe inaccordance with non-limiting embodiments.

FIGS. 9-25 illustrate enlarged views of the distal end of shafts inaccordance with non-limiting embodiments.

FIGS. 16A and 16B illustrate a cross-sectional view of a portion of aretractable safety syringe in a storage position (FIG. 16A) and aworking position (FIG. 16B).

FIGS. 17A and 17B illustrate a cross-sectional view of a portion of aretractable safety syringe in a storage position (FIG. 17A) and aworking position (FIG. 17B).

FIGS. 18 and 19 illustrate a cross-sectional view of a portion of aprefilled retractable safety syringe in a storage position.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a medicalprofessional or user utilizing a syringe to deliver medication to apatient. The term “proximal” refers to the portion of the syringeclosest to the medical professional or user and the term “distal” refersto the portion located furthest from the medical professional or user.It will be further appreciated that for conciseness and clarity, spatialterms such as “vertical,” “horizontal,” “up,” and “down” may be usedherein with respect to the illustrated embodiments. However, syringesmay be used in many orientations and positions, and these terms are notintended to be limiting and absolute.

FIGS. 1-2 illustrate a retractable safety syringe 10 in accordance withone non-limiting embodiment. FIG. 1 is a side view of the retractablesafety syringe 10. FIG. 2 is a cross sectional view of the retractablesafety syringe of FIG. 1 taken along Line 2-2. The retractable safetysyringe 10 has a vacuum chamber 12 that creates a refraction force toretract a needle 14 of the retractable safety syringe 10 within theretractable safety syringe 10 so as to prevent accidental needlepricking and needle reuse. The retractable safety syringe 10 may have asyringe body 16 defining a distal portion 20 and a proximal portion 24.The body 16 may define a fluid chamber 34 fillable with fluidicmedication. As discussed in more detail below, the retractable safetysyringe 10 may be configured as a prefilled syringe. A needle holder 18may be removably engaged to the distal portion 20 of the syringe body16. The needle 14 may be fixedly engaged to the needle holder 18 andprotrude coaxially out of the distal portion 20 of the syringe body 16.The fluid chamber 34 is in fluid communication with the needle 14through the distal end of the fluid chamber 34. The retractable safetysyringe 10 may also have a plunger assembly 37 comprising a piston 26coupled to a rigid shaft 32. In various embodiments, the shaft 32 mayhaving a plurality of components assembled together to form the shaft.In various embodiments, the shaft 32 may be unitary with the piston 26.In various embodiments, the shaft 32 may be joined to the piston 26 viaa threaded engagement, although this disclosure is not so limited. Thepiston 26 may have a punch 70 distally protruding toward the needleholder 18. The plunger assembly 37 is traversable within the syringebody 16 between a refracted position and an engaged position. Generally,the retracted position is when the piston 26 is closer to the proximalportion 24 of the syringe body 16 than the distal portion 20 of thesyringe body 16. But, the retracted position may include situations whenthe piston 26 does not contact the needle holder 18 and the piston 26 iscloser to the distal portion 20 of the syringe body 16 than the proximalportion 24 of the body 16. The engaged position is when the piston 26 isin contact with the needle holder 18 and engaged to the needle holder18.

The shaft 32 may extend out of the syringe body 16 through the proximalportion 24 of the syringe body 16 and may be coaxially aligned with thesyringe body 16. A thumb platform 30 may be attached to the proximalportion of the shaft 32. The thumb platform 30 may be operative totraverse the plunger assembly 37 between the retracted position and theengaged position. The retractable safety syringe 10 may also fingerplatforms 31 extending laterally from the proximal portion 24.

A wedge element 152 may be positioned between the needle holder 18 andthe distal portion 20 to form an airtight and fluid tight sealtherebetween. In particular, the distal portion 20 of the body 16 mayhave a cylindrical nub 21. The needle holder 18 may a correspondingconfiguration as an inner surface 23 of the cylindrical nub 21. Theneedle holder 18 may have a lip 13 (see FIG. 2) to engage the distalportion 20 such that the needle holder 18 is not pushed out the distalportion 20 of the body 16 as a wedge element 152 is traversed to thereleasing position (discussed below).

Various portions of the body 16 may be transparent to allow viewing ofthe fluidic medication by the user. Furthermore, a marked portion 17 mayalso have volume markings, or other indicia, to indicate volume levelswithin the fluid chamber 34. The aspect ratio (i.e., the ratio of theheight to the width) of the fluid chamber 34 for any particularretractable safety syringe 10 may vary based on the intended volume ofmedication to be dispensed. For neonatal embodiments, for example, theaspect ratio of the fluid chamber 34 may be configured to provide theproper resolution to dispense medication in extremely small dosages(e.g., less than 1 cc, or less than 0.5 cc). In other embodiments, theaspect ratio of the fluid chamber 34 may be configured to dispensemedication in larger dosages (e.g., more than 1 cc).

The piston 26 may have an outer diameter similar to the inner diameterof the body 16. The piston 26 may have a piston seal 54 which engages anouter surface of the piston 26 and an inner surface 56 of the body 16.The piston seal 54 may form a watertight and an airtight seal betweenthe piston 26 and the inner surface 56 of the body 16, thus maintaininga barrier between the fluid chamber 34 from the vacuum chamber 12. Thepiston seal 54 may traverse along the inner surface 56 of the body 16 asthe plunger assembly 37 is traversed between the retracted position andthe engaged position.

In various embodiments, the retractable safety syringe 10 may furtherhave a braking mechanism 70 disposed at the proximal portion 24 thatholds the plunger assembly 37 in place between the retracted positionand a filling position prior to engagement of the piston 26 with theneedle holder 18. The filling position when the plunger assembly 37 isbetween the engaged position and the retracted position and the piston26 is closely adjacent the needle holder 18. By way of example and notlimitation, the filling position may be when the piston 26 is in contactwith the needle holder 14 but not engaged to the needle holder 14. FIG.3 is a cross sectional view of the distal end of the retractable safetysyringe 10 illustrating an exploded view of the braking mechanism 70 inaccordance with one non-limiting embodiment. With reference to FIGS. 2and 3, the braking mechanism 70 permits the retractable safety syringe10 to be operated in a substantially similar manner to prior artnon-retracting conventional syringes except that the syringe 10automatically retracts the needle 14 into the body 16 immediately afterfluidic medication has been injected into a patient or user. In priorart non-retracting safety syringes, the piston does not traverse backtoward the refracted position when thumb pressure is released from thethumb platform. The reason is that prior art non-retracting safetysyringes do not have a retraction force acting on the piston. In theillustrated embodiment, the plunger assembly 37 does not traverse backtoward the retracted position when thumb pressure is released from thethumb platform 30 because of the braking mechanism 70. The brakingmechanism 70 of retractable safety syringe 10 counteracts the refractionforce of the vacuum chamber 12 such that the needle 14 does notautomatically retract when thumb pressure is released from a thumbplatform 30.

The braking mechanism 70 may have a cover 72 and a brake member 74 thatare engaged to an attachment base 76. The attachment base 76 may definean inner surface that has a stepped configuration. An upper step 78 mayhave a larger inner diameter compared to an inner diameter of a lowerstep 80. The upper step 78 and the lower step 80 may be joined to eachother via a lip 82. The cover 72 may have an outer diameter sized to fitthe upper step 78. Also, a top surface 84 of the cover 72 may be flushwith a top surface 86 of the attachment base 76. The cover 72 may befixedly attached to the attachment base 76 via sonic welding, adhesiveand other joining methods known in the art. The attachment base 76 maybe fixedly attached to the proximal portion 24 using any suitablejoining technique known in the art, such as spin welding, for example.The cover 72 may have a through-hole 88 through which the shaft 32 maybe disposed and slidingly traversed. An inner surface 90 of the cover 72may have an inner diameter that is smaller than the inner diameter ofthe lower step 80.

The brake member 74 may be disposed and frictionally engaged to thecover 72. The brake member 74 may be split into two or more pieces. Inone embodiment, the brake member 74 is split into two pieces that aremirror configurations of each other. When the brake member 74 isdisposed in the cover 72, an outer diameter of the brake member 74 maybe equal to or slightly greater than the inner diameter of the innersurface 90 of the cover 72. In this manner, the brake member 74frictionally engages the cover 72 and the inner surface 90 of the cover72 biases the brake member 74 inwardly toward the shaft 32. The amountof inward bias may be pre-set by changing the relative sizes of theinner diameter of the cover 72 and the outer diameter of the brakemember 74.

The attachment base 76 may also house a shaft seal 92. In oneembodiment, the shaft seal 92 has a longitudinal flange 94 defining athrough-hole 96 through which the shaft 32 may be disposed and slidinglytraversed. In other embodiments, other types of seals known in the artmay be used for the shaft seal 92, such as an o-ring or a wiper seal,for example. In some embodiments, a combination of seals may be used toform the shaft seal 92. When the shaft 32 is in the working positions,as discussed in more detail below, the shaft seal 92 forms an airtightseal with the shaft 32 in order to maintain a vacuum in the vacuumchamber 12 when the piston 26 is traversed distally from the attachmentbase 76. The longitudinal flange 94 of the shaft seal 92 may flex toexpand or contract the through-hole 96 in order to maintain contact withthe shaft 32.

When the brake member 74 is disposed in the cover 72, the brake member74 is in a braking position. At the braking position, the brake member74 may have a plurality of fingers or projections 100 that inwardlyprotrude toward the shaft 32. The inner surface 88 of the cover 72biases the projections 100 inwardly, and the projections 100 pressagainst the outer surface of the shaft 32 inducing a frictional forcebetween the projections 100 of the brake member 74 and the outer surfaceof the shaft 32. Alternatively, it is also contemplated that the brakemember 74 may have a cylindrical inner surface, or any other suitablyshaped surface. The entire inner surface of the brake member 74 maycontact or press against the outer surface of the shaft 32. Accordingly,it is contemplated that the friction surface of the brake member 74 thatpresses against the outer surface of the shaft 32 may have otherconfigurations to change the amount of inward bias. It is alsocontemplated the amount of friction force between the brake member 74and the outer surface of the shaft 32 may be varied to meet therequirements of the syringe. For example, the inner diameter of theinner surface 90 of the cover 72 may be reduced so as to further biasthe projections 100 against the outer surface of the shaft 32. Thefriction force between the brake member 74 and the shaft 32 may also bevaried by changing the material of the brake member 74 and the shaft 32or having different finishes at the interface of the outer surface ofthe shaft 32 and the friction surface of the brake member 74. Duringoperation, when the brake member 74 is at the braking position (seeFIGS. 16B and 17B), the friction force between the projections 100 ofthe brake member 74 and the shaft 32 is less than the friction forcebetween the brake member 74 and the cover 72. In this manner, the brakemember 74 is not dislodged out of the cover 72 and within the lower step80 (e.g., released position) as the plunger assembly 37 is traversedtoward the filling position or engaged position. The shaft 32 may slideagainst the projections 100 of the brake member 74 as the plungerassembly 37 is traversed between the retracted position and the engagedposition without the brake member 74 being dislodged from the brakingposition due to the frictional forces of the projections 100 of thebrake member 74 and the shaft 32 being less than the frictional forcesof the brake member 74 and cover 72.

The brake member 74 is traversable between the braking position and areleased position. When the brake member 74 is traversed to the releasedposition (see FIG. 6), the brake member 74 is disposed within the lowerstep 80 of the interior cavity of the attachment base 76. The innersurface 90 of the cover 72 no longer biases the projections 100 inwardlyto press the projections 100 of the brake member 74 against the shaft 32creating the frictional force that counteracts the retraction force ofthe vacuum chamber 12. At the released position, the brake member 74 isloose because the lower step 80 defines a larger volume and the brakemember 74 such that the brake member 74 falls apart, or otherwiseexpands, when disposed within the lower step 80. The projections 100 donot press against the outer surface of the shaft 32 and does not produceany counteracting forces such that the plunger assembly 37 may be freelyretracted toward the retracted position when the user releases the thumbplatform 30.

To traverse the brake member 74 from the braking position to thereleased position, the plunger assembly 37 may be formed with a ram 33which initially contacts an upper surface 109 (see FIG. 3) of the brakemember 74 and pushes the brake member 74 out of the cover 72 and withinthe lower step 80. More particularly, when the plunger assembly 37 istraversed toward the engaged position, a lower surface 108 of the ram 33contacts the upper surface 109 of the brake member 74. As the plungerassembly 37 is further traversed to the engaged position, the ram 33continues to push downwardly on the brake member 74 urging the brakemember 74 off of the inner surface 90 of the cover 72 and within thelower step 80. An outer diameter of the ram 33 may be smaller than aninner diameter of the through-hole 88 of the cover 72 such that there isno frictional engagement between the ram 33 and the cover 72. As shownin FIGS. 1-3, the ram 33 may be integrally formed with the shaft 32 andthe thumb platform 30 such that the ram 33 is formed as part of theplunger assembly 37 in general. In some embodiments, the ram 33 may beformed with the thumb platform 30, and the thumb platform 30 may have areceiver portion that receives a proximal portion of the shaft 32.

In use, the braking mechanism 74 prevents the plunger assembly 37 fromretracting toward the retracted position during operation of the syringeas long as the brake member 74 is maintained at the braking position.The user may release the thumb platform 30 without any concern that theplunger assembly 37 will be traversed back toward the retracted position

The retractable safety syringe 10 may be prefilled and shipped andultimately provided to a medical professional or user with the plungerassembly 37 in a storage position (as shown in FIG. 2) with fluidicmedication contained within the variable fluid chamber 34.Alternatively, the retractable safety syringe 10 may be shipped andultimately provided to a medical professional or user with the plungerassembly 37 in a storage position (see FIGS. 16A and 17A) withoutfluidic medication contained within the variable fluid chamber 34.

FIG. 4 is a perspective view of the piston 26 in accordance with onenon-limiting embodiment. FIG. 5 is a perspective view of the piston 26of FIG. 4 taken along a longitudinal axis (illustrated as “A”).Referring now to FIGS. 2, and 4-5, by way of example and not limitation,when the needle holder 18 is engaged to the distal portion 20, a wedgeelement 152 may be in frictional contact with the needle holder 18. Thepiston 26 may have a punch 70 distally protruding toward the needleholder 18. The punch 70 may be a substantially hollow cylinder. In oneembodiment the punch 70 is equipped with an upper proximal block tab 73extending around less than about one-half of the circumference of thesubstantially hollow cylinder, and a lower distal wedge tab 75 extendingaround less than about one-half of the circumference of thesubstantially hollow cylinder and located opposite the upper block tab73. During the engagement process, the punch 70 may distally push thewedge element 152 and engage the needle holder 18. The lower distalwedge tab 75 passes and hooks onto the needle holder 18 (e.g., a lip ofthe needle holder) when the plunger assembly 37 is traversed to theengaged position. After engagement, the needle body 18 and needle 14 arewithdrawn into the syringe body 16 via the retraction force. The punch70 may also define a cutout 71 positioned longitudinally proximal toupper proximal block tab 73 and a ramp 77 positioned longitudinallyproximal to lower distal wedge tab 75. When the needle body 18 and theneedle 14 are retracted, the ramp 77 may laterally bias the needle body18 and the cutout 71 may receive a portion of the needle body 16 to cantthe needle 16 toward one side of the syringe body 16. FIG. 6 illustratesa retractable safety syringe 10 at the completion of the operationalstroke.

FIGS. 7-8 illustrate the shaft 32 in accordance with variousnon-limiting embodiments. The shaft 32 illustrated in FIGS. 7-8 may beused, for example, with a prefilled syringe. The shaft 32 may have athreaded portion 40 to engage the piston 54 (FIG. 2). The shaft 32 hasan engaging portion 42 and a non-engaging portion 44. As illustrated,the engaging portion 42 may be discontinuous along the longitudinalaxis. For example, the engaging portion 42 may comprise a first engagingportion 42 a and a second engaging portion 42 b. The non-engagingportion 44 may also be discontinuous along the longitudinal axis. Forexample, the non-engaging portion 44 may comprise a first non-engagingportion 44 a and a second non-engaging portion 44 b (FIG. 7). A thirdengaging portion 44 c may be positioned intermediate the firstnon-engaging portion 44 a and the second non-engaging portion 44 b.

The engaging portion 42 has an outer diameter that is sized to engagethe shaft seal 92 (FIG. 2) and form an airtight barrier when theengaging portion 42 is positioned proximate the shaft seal 92. The outerdiameter of the engaging portion 42 may be at least slightly greaterthan the inner diameter of the through-hole 96 (FIG. 2) of the shaftseal 92. The engaging portion 42 is also sized to frictionally engagethe brake member 74 when the engaging portion 42 is positioned proximatethe brake member 74. Thus, the engaging portion 42 is generally theportion of the shaft 32 that either engages the shaft seal 92 orfrictionally engages the brake member 74. The non-engaging portion 44has an outer diameter that is sized such that an airtight seal is notformed (e.g., a non-sealing engagement) when positioned proximate theshaft seal 92 (FIG. 2). The outer diameter of the non-engaging portion44 may be less than the inner diameter of the through-hole 96 (FIG. 2)of the shaft seal 92. In some embodiments, the outer diameter of thenon-engaging portion 44 is substantially similar to the inner diameterof the through-hole 96 of the shaft seal 92 such that only nominalcontact is made between the shaft seal 92 and non-engaging portion 44,but an airtight seal is not formed. The non-engaging portion 44 is alsosized such that there is no frictional engagement, or at least only aminimal frictional engagement between the brake member 74 and thenon-engaging portion 44 when the engaging portion 42 is positionedproximate the brake member 74. As discussed in more detail below, bylimiting the amount of force exerted on the shaft seal 92 and the brakemember 74, the shelf life of the retractable safety syringe 10 isextended. Since the syringe 10 may be stored with little or no-load onsensitive internal components, the syringe 10 can also endure variousenvironmental conditions during extended periods of storage (e.g.,changes in temperature) without the components failing or otherwisedeforming.

Still referring to FIGS. 7-8, the outer diameter of the non-engagingportion 44 is less than the outer diameter of the engaging portion 42.The particular diameters of these portions for any particularimplementation may be at least partially dependent on the size of theassociated syringe and the inner diameters of the shaft seal 92 and thebrake member 74. For example in one non-limiting embodiment, the outerdiameter of the engaging portion 42 may be about 0.125 inches and theouter diameter of the non-engaging portion 44 may be about 0.085 inches.In other embodiments, the outer diameter of the engaging portion 42 maybe larger or smaller than 0.125 inches and the outer diameter of thenon-engaging portion 44 may be larger or smaller than 0.085 inches. Insome embodiments, the outer diameter of the engaging portion 42 may be amultiple of the outer diameter of the non-engaging portion 44. Forexample, in one embodiment, the outer diameter of the engaging portion42 is at least 1.1 times the outer diameter of the non-engaging portion44. In one embodiment, the outer diameter of the engaging portion 42 isat least 1.3 times the outer diameter of the non-engaging portion 44. Inone embodiment, the outer diameter of the engaging portion 42 is atleast 1.6 times the outer diameter of the non-engaging portion 44. Inone embodiment, the outer diameter of the engaging portion 42 is atleast 2 times the outer diameter of the non-engaging portion 44. In oneembodiment, the outer diameter of the engaging portion 42 is at least 3times the outer diameter of the non-engaging portion 44. In someembodiments, the outer diameters of the first engaging portion 42 a andthe second engaging portion 42 b may differ. In some embodiments, theouter diameters of the first non-engaging portion 44 a and the secondnon-engaging portion 44 b may differ. Accordingly, this disclosure isnot limited to any particular diameter configuration of non-engaging andengaging portions of the shaft.

Still referring to FIGS. 7-8, the non-engaging portion 44 may belongitudinally positioned along the shaft 32 at any suitable location,included the distal end of the shaft 32. As discussed in more detailbelow, the position of the non-engaging portion 44 may be based on thetotal volume of the fluid chamber 34 and amount of prefilled medicationcontained by the fluid chamber 34. As illustrated, the second engagingportion 42 b may be positioned intermediate the non-engaging portion 44and the piston 26 (FIG. 2). The longitudinal offset of the non-engagingportion 44 from the distal end of the shaft 32 may vary. In someembodiments, the non-engaging portion 44 is longitudinally positionedapproximately 0.5 inches from the piston 26. Such an arrangement may beused, for example, with a 5 cc syringe that is prefilled with 3 cc ofmedication.

The retractable safety syringe 10 may shipped and/or stored when theplunger assembly 37 is in a storage position. In the storage position(see e.g., FIG. 2), the shaft 32 is not placing a potentiallydestructive load on either the shaft seal 92 or the brake member 74.Accordingly, the retractable safety syringe 10 can be stored in thisposition for relatively long periods of time without degradation ordeformation of the components within the retractable safety syringe 10that could affect the functionality of the syringe, thereby increasingits storage life. When a user either distally or proximally translatesthe plunger assembly 37, the plunger assembly 37 is moved out of thestorage position and into the working positions. Thus, the workingpositions include all of the positions of the plunger assembly 37 thatrely on a seal between the shaft 32 and the vacuum chamber 12 and/or africtional engagement between the shaft 32 and the brake member 74 forproper operation. For example, the working positions of the plungerassembly 37 may include the various positions of the plunger assemblyduring the dispensing of the fluidic medication and the retraction ofthe needle 14 into the syringe body 16 via the vacuum retraction force.The length of the non-engaging portion may be at least slightly greaterthan the longitudinal separation of the shaft seal 92 and the brakemember 74. For example, the non-engaging portion may be about 0.2″ inlength. In embodiments having multiple non-engaging portions 44 (FIG.7), the sizing of each of the non-engaging portions 44 may depend on thesize of the component that the non-engaging portion 44 is proximate tooin the storage position. For example, for embodiments having a brakemember 74 with a longitudinal dimension of about 0.12″, the firstengaging portion 42 a may be longitudinally spaced from the thirdengaging portion 42 c at a distance greater than 0.12″. Similarly, forembodiments having a shaft seal 92 with a longitudinal dimension ofabout 0.07″, the third engaging portion 42 c may be longitudinallyspaced from the second engaging portion 42 b at a distance greater than0.07″. As is to be appreciated, in various embodiments, the spacing andarrangement of the engaging portions and non-engaging portions along theshaft may vary based on application.

FIGS. 9-15 illustrated enlarged views of the distal end of the shaft 32in accordance with various non-limiting embodiments. Referring to FIG.9, the transitions between the non-engaging portion 44 and the engagingportions 42 may be beveled. According to various embodiments, the bevels(e.g., tapers) may comprise curved portions, linear portions, or acombination of curved and linear portions. The first bevel 60 a servesas a transition from the first engaging portion 42 a to the non-engagingportion 44 and a second bevel 60 b serves as a transition from thenon-engaging portion 44 to the second engaging portion 42 b. The bevels60 generally aid in the operation of the retractable safety syringe 10as the plunger assembly 37 is translated between the storage positionand the working positions. For example, the bevel 60 helps to reduce thelikelihood that the engaging portion 44 undesirably dislodges the brakemember 74 as the engaging portion 42 a comes in contact with the brakemember 74 during the operational stroke.

The angle of the bevel 60 may be any suitable angle. For example, Θ₁(FIG. 9) may be approximately 50 degrees, although this disclosure isnot so limited. In some embodiments, Θ₂ (FIG. 10) may be approximately75 degrees, although this disclosure is not so limited. The particularangle of the bevel 60 may be based on, for example, manufacturingmethods, the type of shaft seal 92, and/or the configuration of thebrake member 74. FIG. 11 illustrates first and second bevels 60 a, 60 bthat are generally curved in accordance with one non-limitingembodiment. The first bevel 60 a has a curved section having a radius‘r₁.’ The second bevel 60 b has a curved section having a radius ‘r₂.’In this embodiment the first bevel 60 a provides for a more graduatedtransition between the first engaging portion 42 a and the non-engagingportion 44 as compared to the second bevel 60 b.

FIG. 12 illustrates the distal end of the shaft 32 in accordance withanother non-limiting embodiment. The shaft 32 comprises a firstnon-engaging portion 44 a having a larger outer diameter than a secondnon-engaging portion 44 b. The shaft 32 has a first bevel 60 a thattransitions between the first engaging portion 42 a and the firstnon-engaging portion 44 a and a second bevel 60 b that transitionsbetween the first non-engaging portion 44 a and the second non-engagingportion 44 b. A lip 64 serves as the transition between the secondnon-engaging portion 44 b and the second engaging portion 42 b. FIG. 13illustrates an embodiment of the shaft 32 comprising a bevel 60transitioning between the first engaging portion 42 a and a non-engagingportion 44 and a lip 64 serves as the transition between thenon-engaging portion 44 and the second engaging portion 42 b. FIGS. 14and 15 illustrate embodiments of the shaft 32 that have the non-engagingportion 44 positioned proximate the distal end of the shaft 32. Asillustrated, the bevels 60 may be any suitable configuration. Forexample, the first bevel 60 a allows for a more gradual transition thanthe second bevel 60 b. As illustrated in FIG. 15, the third bevel 60 cis curved and has a radius ‘r₃.’

FIGS. 16A and 16B illustrate a cross-sectional view of a portion of theretractable safety syringe 10 in a storage position (FIG. 16A) and aworking position (FIG. 16B) in accordance with one non-limitingembodiment. Referring first to FIG. 16A, the non-engaging portion 44 isproximate the shaft seal 92 and the brake member 74 while in the storageposition. The shaft 32 and the shaft seal 92 do not form an air-tightseal (e.g., a non-sealing engagement) in the storage position.Therefore, the shaft 32 does not contact the shaft seal 92, or at leastonly nominally contacts the shaft seal 92 in this position. Similarly,the shaft 32 is not in frictional engagement with the brake member 74.If any contact is made between the brake member 74 and the non-engagingportion 44, it is only nominal such that it will not affect theperformance of the brake member 74 if such contact is maintained for along period of time. As is to be appreciated, the amount of contactbetween the shaft seal 92 and/or the brake member 74 may depending onthe particular implementation of these components. For example, if theshaft seal 92 is an o-ring, the o-ring may be generally able towithstand a greater force than a molded wipe seal. Similarly, if thebrake member 74 is hardened plastic, for example, it may be able towithstand more force than a resilient rubber brake member. In any event,the combination of components is arranged such that the retractablesafety syringe 10 may be maintained in the storage position forrelatively long periods of time, at various temperatures, and variousatmospheric pressures, without substantial deformation of the shaft seal92 and or the brake member 74. Therefore, when a user ultimatelytranslates the shaft 32 after a period of storage, the seal 92 and brakemember 74 will function properly.

Referring now to FIG. 16B, the retractable safety syringe 10 isillustrated in a working position after the plunger assembly 37 has beendistally translated. In the working position, the engaging portion 42 isproximate the shaft seal 92 and the brake member 74. The engagementbetween the engaging portion 44 and the shaft seal 92 forms an airtightbarrier for the vacuum chamber 12. The frictional engagement between thebrake member 74 and the engaging portion 44 allows the user to removetheir thumb from the thumb platform 30 (FIG. 2) without the plungerassembly 37 being drawn in the proximal direction due to the vacuumforce of the vacuum chamber 12 upon the piston 26.

FIGS. 17A and 17B illustrate a cross-sectional view of a portion of theretractable safety syringe 10 in a storage position (FIG. 17A) and aworking position (FIG. 17B) in accordance with one non-limitingembodiment. As illustrated, the shaft 32 has multiple non-engagingportions 44. In the storage position shown in FIG. 17A, the firstnon-engaging portion 44 a is positioned proximate the brake member 74and the second non-engaging portion 44 b is proximate the shaft seal 92.By having an engaging portion 44 c positioned intermediate the firstnon-engaging portion 44 a and the second non-engaging portion 44 b,incidental translation of the plunger assembly 37 may be eliminated, orat least reduced, while the syringe is in the storage position.Referring now to FIG. 17B, the retractable safety syringe 10 isillustrated in a working position after the plunger assembly 37 has beendistally translated. In the working position, the engaging portion 42 ais proximate the shaft seal 92 and the brake member 74 allowing forproper operation of the retractable safety syringe 10.

FIG. 18 illustrates a portion of a prefilled retractable safety syringe200 in its storage position in accordance with one non-limitingembodiment. The prefilled retractable safety syringe 200 may begenerally similar to the retractable safety syringe 10, accordinglysimilar reference numbers are used to identify similar components. Theprefilled retractable safety syringe 200 may be shipped or stored withfluid in the fluid chamber 12 without the shaft seal 92 and the brakemember 74 under a substantial load.

In this embodiment, the non-engaging portion 44 is proximally offsetfrom the piston 26, similar to the shaft 32 illustrated in FIG. 8. Thevolume of the fluid chamber 34 when the prefilled retractable safetysyringe 200 is in the storage position is therefore a function of thelongitudinal distance (illustrated as ‘d’) between the piston 26 and thenon-engaging portion 44 of the shaft 32. As the longitudinal distance‘d’ increases, the volume of the fluid chamber 34 in the storageposition will decrease. In various embodiments, the location of thenon-engaging portion 44 along the shaft 32 is determined by the amountof fluidic medication that will be stored in the fluid chamber 34 duringshipment. In any event, the syringe may be shipped with the piston 26located at a position in between the proximal end 24 and the distal end20, as opposed to being drawn toward the proximal end 24 of theprefilled retractable safety syringe 200.

By way of example, for a 5 cc syringe that will be shipped with 3 cc ofmedication, the longitudinal distance ‘d’ between the piston 26 and thenon-engaging portion 44 will be a first distance. If the same syringewas to be shipped with 4 cc of medication, the longitudinal distance ‘d’between the piston 26 and the non-engaging portion 44 will be a seconddistance, where the second distance is less than the first distance. Asis to be appreciated, the longitudinal distance ‘d’ could still besimilar between these two implementations if the diameter of the barrel16 was increased for the 4 cc implementation.

While the plunger assembly 37 is in the storage position, the vacuumchamber 12 is generally at the same pressure as the atmospheric pressuresince the shaft seal 92 is not in a sealing engagement with the shaft32. Once the plunger assembly 37 is distally translated, an air-tightseal is formed between the engaging portion 42 a and the shaft seal 92to generate vacuum with in the vacuum chamber necessary for the properoperation of the prefilled retractable safety syringe 200

FIG. 19 illustrates another embodiment of the prefilled retractablesafety syringe 200 shown in the storage position. This embodimentutilizes the shaft 32 illustrated in FIG. 7 having a first non-engagingportion 44 a and a second non-engaging portion 44 b. The firstnon-engaging portion 44 a is positioned proximate the brake member 74and the second non-engaging portion 44 b is positioned proximate theshaft seal 92. The third engaging portion 42 c is disposed intermediatethe brake member 74 and the shaft seal 92. The third engaging portion 42c has an outer diameter that is larger than the inner diameter of theshaft seal 92 and the inner diameter of the brake member 74. Thus, whilethe third engaging portion 42 c can be passed through the shaft seal 92and/or the brake member 74 during the operational stroke of the syringe,the frictional force must be overcome by the user. If the prefilledretractable safety syringe 200 is merely subjected to reducedatmospheric pressures, such as during an air shipment, an expansion ofan air bubble in the liquid chamber 34 (FIG. 2) will not impartsufficient force upon the piston 26 to overcome the frictional forcebetween the third engaging portion 42 c and the brake member 74.Therefore, in the storage position, the plunger assembly 37 is generally“locked” into place and unwanted stopper movement is reduced, if noteliminated. By locking the plunger assembly 37 in place, the chances ofa sterility failure of the prefilled syringe during shipment is greatlyreduced.

With reference now to the operation of the retractable safety syringeillustrated in FIG. 2, during an operational stroke, the vacuum chamber12 is enlarged upon movement of the plunger assembly 37 toward thedistal portion 20 such that the internal volume of the vacuum chamber 12is increased. Movement of the plunger assembly 37 out of the storageposition (FIG. 2) and into a working position (see e.g., FIGS. 16B and17B) seals the vacuum chamber 12 and a vacuum created within the vacuumchamber 12 may exert a retraction force upon the plunger assembly 37. Aswill be understood by one of skill, the retraction force may be exertedupon the shaft 32 indirectly via exertion upon the proximal surface ofthe piston 26. The retraction force may vary as the plunger assembly 37moves toward the distal portion 20 or toward the proximal portion 24.Thus, the retraction force may increase or decrease, respectively. Theretraction force may be exerted on the plunger assembly 37 directed fromthe distal portion 20 toward the proximal portion 24. The retractionforce may be caused due to a vacuum pressure in the vacuum chamber 12.

When the retractable safety syringe 10 is in the filling position, theneedle 14 may be inserted into a medication container containing fluidicmedication. The medical professional or user may slip his or her fingersunderneath the thumb platform 30 and pull the thumb platform 30 awayfrom the syringe body 16. Note that even though the vacuum chamber 12 isexerting a vacuum force on the piston 26 when the retractable safetysyringe 10 is in the filling position, the force exerted by the brakemember 74 on the shaft 32 exceeds the vacuum force. As the plungerassembly 37 is traversed toward the retracted position, the fluid withinthe medication container is transferred into the fluid chamber 34 viathe needle 14. When the appropriate amount of fluidic medication isfilled in the variable fluid chamber 34, the user stops traversing thethumb platform 30 away from the syringe body 16. The user or medicalprofessional removes the needle 14 from the medication container. Asmall amount of air may be trapped within the variable fluid chamber 34.To remove the trapped air, the user or medical professional may invertthe retractable safety syringe 10 such that the needle 14 is pointedupwardly. The user or medical professional taps the outside surface ofthe syringe body 16 to urge the trapped air within the fluid chamber 34toward the needle tip. The medical professional or user may place his orher first and second fingers underneath the finger platforms 31 andplace his or her thumb on the thumb platform 30. When the thumb platform30 is depressed to remove the trapped air within the fluid chamber 34, aretraction force is created by the vacuum chamber 12 when the plungerassembly 37 is traversed toward the engaged position to remove trappedair within the variable fluid chamber 34. The force exerted by the brakemember 74 on the shaft 32 exceeds the retraction force, thereby allowingthe medical professional or user to remove their thumb from the thumbplatform 30, if necessary.

At this moment, the retractable safety syringe 10 has been prepared toinject the fluidic medication into a patient. In one embodiment, theretractable safety syringe 10 may be prefilled and delivered to the useror medical professional with a predetermined amount of fluidicmedication. In any event, the needle 14 is inserted into the patient andthe plunger assembly 37 is traversed from the retracted position to theengaged position. The user or medical professional traverses the plungerassembly 37 from the retracted position to the engaged position byplacing his or her first and second fingers under the finger platforms31 and his or her thumb on the thumb platform 30. As the vacuum chamber12 is enlarged it produces a retraction force which urges the plungerassembly toward the retracted position. When the plunger assembly 37 istraversed to the engaged position, the piston 26 may engage the needleholder 18 and needle 14. As the plunger assembly 37 is traversed to theengaged position, the ram 33 contacts the brake member 74 and pushes thebrake member 74 out of the cover 72 and within the lower step 80 (seeFIG. 3). With the brake member 74 pushed from the cover 72, the brakemember no longer applies a braking force to the shaft 32.

Once the piston 26 engages the needle holder 18 and needle 14, the useror medical professional may release pressure on the thumb platform 30such that the retraction force is greater than the thumb pressure andthe plunger assembly 37 is urged back toward the retracted position (seeFIG. 6). The needle holder 18 and needle 14 are urged back into body 16thereby covering the needle 14 and preventing accidental needleprickings and needle reuse. Also, the needle 14 may be canted toward oneside of the syringe body 16. Canting the needle 14 toward one side ofthe syringe body 16 keeps the needle 14 from accidentally protrudingthrough the distal end of the syringe body 16.

The piston 26 may be engageable to the needle holder 18 and needle 14via any method known in the art. By way of example and not limitation,the piston 26 may be engageable to the needle holder 18 and needle 14via the structure disclosed in U.S. Pat. No. 6,413,236, the entirecontent of which is expressly incorporated herein by reference. Thepiston 26 may be engageable to the needle holder 18 and needle 14 viathe structure disclosed in concurrently filed application Ser. No.12/842,885 entitled “MULTI-CHAMBERED RETRACTABLE SAFETY SYRINGE” andfiled Jul. 23, 2010, the entire disclosure of which is expresslyincorporated herein by reference.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments. The dimensions and values disclosed hereinare not to be understood as being strictly limited to the exactnumerical values recited. Instead, unless otherwise specified, each suchdimension is intended to mean both the recited value and a functionallyequivalent range surrounding that value. For example, a dimensiondisclosed as “40 mm” is intended to mean “about 40 mm”.

The invention claimed is:
 1. A retractable safety syringe for preventingaccidental needle pricking and needle reuse after completion of aninjection stroke, the syringe comprising: a syringe body defining aproximal portion and a distal portion; a seal located in the proximalportion of the syringe body; a needle coupled to a needle holder, theneedle holder removeably engageable to the body distal portion; a pistondisposed within the body and biasable to the body proximal portion via avacuum force when the piston is traversed toward the body distalportion, the piston being traverseable between a retracted position andan engaged position; a vacuum chamber disposed within the syringe body,the vacuum chamber located intermediate the piston and the seal, thevacuum chamber configured to provide a vacuum force on the piston in adirection from the syringe body distal portion toward the syringe bodyproximal portion upon movement of the piston toward the syringe bodydistal portion responsive to the distal translation of the piston; afluid chamber disposed within the syringe body, the fluid chamberlocated distally from the piston, the fluid chamber having a distal andproximal end, the proximal end of the fluid chamber being sealed, thefluid chamber in fluid communication with the needle through the distalend of the fluid chamber and configured to be reduced in volume as thepiston is traversed towards the engaged position; and a shaft attachedto the piston and disposed within the body, the shaft comprising anengaging portion and a non-engaging portion, the shaft extending throughthe proximal portion of the body and proximate the seal, traversal ofthe shaft though the body operative to traverse the piston within thesyringe body between a storage position and working positions, theengaging portion proximate the seal and in sealing engagement with theseal in the working positions and the non-engaging portion proximate theseal and in a substantially non-sealing engagement with the seal in thestorage position.
 2. The retractable safety syringe of claim 1, whereinthe engaging portion has a first outer diameter and the non-engagingportion has a second outer diameter, wherein the first outer diameter isgreater than the second outer diameter.
 3. The retractable safetysyringe of claim 2, wherein the shaft comprises a beveled transitionbetween the engaging portion and the non-engaging portion.
 4. Theretractable safety syringe of claim 1, further comprising: a firstcavity positioned proximate the body proximal portion; and a brakemember disposed in the first cavity of the body, the brake memberproximate the non-engaging portion and in a substantially non-frictionalengagement with the brake when the shaft is in the storage position, thebrake member biased toward and frictionally engaged to the engagingportion for providing a braking force to maintain a position of thepiston within the syringe body before completion of the injection strokewhen the shaft is in the working positions, the brake member completelydisengaged from the shaft after completion of the injection stroke byaxially traversing the brake member into the second cavity so the vacuumforce withdraws the needle into the syringe body to prevent accidentalneedle pricking and needle reuse.
 5. The syringe of claim 4, wherein theseal and the brake member are separate components.
 6. The retractablesafety syringe of claim 1, wherein the non-engaging portion ispositioned intermediate the piston and the engaging portion.
 7. Theretractable safety syringe of claim 6, wherein the non-engaging portionis less than about 0.5 inches in length along a longitudinal axis of theshaft.
 8. The retractable safety syringe of claim 1, wherein theengaging portion comprises a first engaging portion and a secondengaging portion, wherein the non-engaging portion is disposedintermediate the first engaging portion and the second engaging portion,and wherein the second engaging portion is positioned intermediate thepiston and the non-engaging portion.
 9. The retractable safety syringeof claim 8, wherein the first engaging portion is less than about 1 inchin length along a longitudinal axis of the shaft.
 10. The retractablesafety syringe of claim 8, wherein the shaft comprises a first beveledtransition between the first engaging portion and the non-engagingportion and a second beveled transition between the non-engaging portionand the second engaging portion.
 11. The retractable safety syringe ofclaim 8, wherein the first engaging portion is proximate the seal and insealing engagement with the seal in the working positions.
 12. Theretractable safety syringe of claim 1, wherein the piston issubstantially maintained in a stationary position when the piston is inthe storage position.
 13. The syringe of claim 1, wherein the syringe isa prefilled syringe, and the piston is in the retracted position whenthe piston and the shaft are in the storage position.
 14. A retractablesafety syringe for preventing accidental needle pricking and needlereuse after completion of an injection stroke, the syringe comprising: asyringe body having a cavity and defining a proximal portion and adistal portion; a seal located in the proximal portion of the syringebody; a brake member disposed in the cavity of the body; a needlecoupled to a needle holder, the needle holder removeably engageable tothe body distal portion; a piston disposed within the body and biasableto the body proximal portion via a vacuum force when the piston istraversed toward the body distal portion, the piston being traverseablebetween a retracted position and an engaged position; a vacuum chamberdisposed within the syringe body, the vacuum chamber locatedintermediate the piston and the seal, the vacuum chamber configured toprovide a vacuum force on the piston in a direction from the syringebody distal portion toward the syringe body proximal portion uponmovement of the piston toward the syringe body distal portion responsiveto the distal translation of the piston; a fluid chamber disposed withinthe syringe body, the fluid chamber located distally from the piston,the fluid chamber having a distal and proximal end, the proximal end ofthe fluid chamber being sealed, the fluid chamber in fluid communicationwith the needle through the distal end of the fluid chamber andconfigured to be reduced in volume as the piston is traversed towardsthe engaged position; and a shaft coupled to the piston and disposedwithin the body, the shaft comprising an engaging portion, a firstnon-engaging portion, and a second non-engaging portion, and extendingthrough the proximal portion of the body and proximate the seal,traversal of the shaft though the body operative to traverse the pistonwithin the syringe body between a storage position and workingpositions, the engaging portion proximate the seal and in sealingengagement with the seal in the working positions; the firstnon-engaging portion proximate the seal and in a substantiallynon-sealing engagement with the seal in the storage position, and thesecond non-engaging portion proximate the brake member and in asubstantially non-frictional engagement with the brake when the shaft isin the storage position.
 15. The retractable safety syringe of claim 14,the engaging portion has a first outer diameter, the first non-engagingportion has a second outer diameter, and the second non-engaging portionhas a third outer diameter, wherein the first outer diameter is greaterthan each of the second and third outer diameters.
 16. The retractablesafety syringe of claim 14, wherein the engaging portion comprises anintermediate engaging portion disposed intermediate the firstnon-engaging portion and the second non-engaging portion.
 17. Theretractable safety syringe of claim 16, wherein the engaging portioncomprises a distal engaging portion positioned intermediate the pistonand the first non-engaging portion.
 18. The retractable safety syringeof claim 17, wherein the distal engaging portion is less than about 1inch in length along a longitudinal axis of the shaft.
 19. Theretractable safety syringe of claim 14, wherein the shaft comprises afirst beveled transition between the non-engaging portion andintermediate engaging portion, a second beveled transition between theintermediate engaging portion and the second non-engaging portion, and athird beveled transition between the second non-engaging portion and theengaging portion.
 20. The retractable safety syringe of claim 19,wherein an angle of at least one of the first and second beveledtransitions is greater than the angle of the third beveled transition.21. The retractable safety syringe of claim 14, wherein the piston issubstantially maintained in a stationary position when the piston is inthe storage position.
 22. The syringe of claim 14, wherein the syringeis a prefilled syringe, and the piston is in the retracted position whenthe piston and the shaft are in the storage position.
 23. The syringe ofclaim 14, wherein the seal and the brake member are separate components.24. A method of operating an automatically retracting syringe, themethod comprising: receiving a syringe comprising: a syringe bodydefining a proximal portion and a distal portion; a fluid chamber withinthe syringe body; a needle coupled to a needle holder, the needle holderremoveably engaged to the distal portion of the syringe body; a seallocated in the proximal portion of the syringe body; a shaft coupled toa piston, the shaft comprising at least one engaging portion and atleast one non-engaging portion, the piston disposed in a storageposition within the syringe body, the piston substantially maintained inthe storage position by the at least one engaging portion of the shaft,the non-engaging portion positioned proximate the seal and insubstantial non-sealing engagement; a vacuum chamber within the syringebody configured to urge the piston toward the retracted position;depressing a thumb platform to traverse the piston toward the distalportion of the syringe during an injection stroke; inducing a biasingforce on the piston via the vacuum chamber to urge the piston assemblyback toward the retracted position; engaging the piston to the needleholder upon completion of the injection stroke; disengaging the needleholder from the syringe body; removing thumb pressure on the thumbplatform; and traversing the needle holder, and the needle into thesyringe body under the biasing force.
 25. The method of operating anautomatically retracting syringe of claim 24, further comprising:distally translating the non-engaging portion away from the seal whenthe thumb platform is depressed.
 26. The method of operating anautomatically retracting syringe of claim 24, wherein the fluid chamberis at least partially filled with fluidic medication when the syringe isreceived.
 27. A retractable safety syringe for preventing accidentalneedle pricking and needle reuse after completion of an injectionstroke, the syringe comprising: means for holding a volume of fluidicmedication; means for expelling the fluidic medication from the holdingmeans through a needle, wherein the expelling means is moveable betweena first storage position and a second working position during aninjection stroke; means for sealing a vacuum chamber; means forpreventing a substantial load on the sealing means when the expellingmeans is in the first storage position; and means for engaging thesealing means in a sealed engagement during an injection stroke when theexpelling means is in the second position.
 28. The retractable safetysyringe of claim 27, comprising: means for braking the expelling means,separate from the means for sealing; means for preventing a substantialload on the braking means when the expelling means is in the firstposition; and means for engaging the braking means in a frictionalengagement when the expelling means is in the second position.
 29. Thesyringe of claim 27, wherein the syringe is a prefilled syringe and themeans for expelling is in a retracted position in the storage position.